The reason El Salvador adopted it is to lower remittance fees. The system of banks and 3rd party overseerers resulted in large fees most weren't able to afford, and if they did, they lost a huge chunk of their money. These ATM is great step to support bitcoin.
That is without a doubt one of the reasons but at the same time there is no doubt that they are looking at the long term and they are thinking that it would be fantastic for them if people that are big on cryptocurrencies and businesses decided that they want to establish themselves at El Salvador and bring a huge deal of foreign investment to the country.
This is not a bad strategy at all and if they can endure the pressure of the international community and keep going forward with this then El Salvador could become a destination for many people that have adopted cryptocurrencies and bring great prosperity to the country.